Abstract
Jet multiplicity distributions in top quark pair ({{rm t}}{rm {overline{t}}}) events are measured in pp collisions at a centre-of-mass energy of 8 TeV with the CMS detector at the LHC using a data set corresponding to an integrated luminosity of 19.7,text {fb}^text {-1}. The measurement is performed in the dilepton decay channels (mathrm {e}^+mathrm {e}^-, mathrm {mu ^+}mathrm {mu ^-}, and mathrm {e}^{pm }mathrm {mu }^{mp }). The absolute and normalized differential cross sections for mathrm {t}overline{mathrm {t}} production are measured as a function of the jet multiplicity in the event for different jet transverse momentum thresholds and the kinematic properties of the leading additional jets. The differential mathrm {mathrm {t} overline{mathrm {t}} mathrm {b}} and mathrm {mathrm {t} overline{mathrm {t}} mathrm {b} overline{mathrm {b}}} cross sections are presented for the first time as a function of the kinematic properties of the leading additional mathrm {b} jets. Furthermore, the fraction of events without additional jets above a threshold is measured as a function of the transverse momenta of the leading additional jets and the scalar sum of the transverse momenta of all additional jets. The data are compared and found to be consistent with predictions from several perturbative quantum chromodynamics event generators and a next-to-leading order calculation.
Highlights
Precise measurements of tt production and decay properties [1,2,3,4,5,6,7,8,9] provide crucial information for testing the expectations of the standard model (SM) and of calculations in the framework of perturbative quantum chromodynamics (QCD) at high-energy scales
The measurements are compared to the predictions from mc@nlo interfaced with herwig6 and from powheg with
Data are compared with predictions from MadGraph interfaced with pythia6, mc@nlo interfaced with herwig6, and powheg intefarced with both pythia6 and herwig6, normalized to the measured inclusive cross section
Summary
Precise measurements of tt production and decay properties [1,2,3,4,5,6,7,8,9] provide crucial information for testing the expectations of the standard model (SM) and of calculations in the framework of perturbative quantum chromodynamics (QCD) at high-energy scales. A correct description of these events is relevant because tt+jets processes constitute important backgrounds in the searches for new physics These processes constitute a challenging background in the attempt to observe the production of a Higgs boson in association with a tt pair (ttH), where the Higgs boson decays to a bottom (b) quark pair (bb), because of the much larger cross section compared to the ttH signal. The ttbb and ttb (referred to as “ttbb (ttb)” in the following) cross sections are measured for the first time differentially as a function of the properties of the additional jets associated with b quarks, which will hereafter be called b jets.
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